1. Field of the Invention
The invention relates to an ultrasonic flow switch.
2. Description of Related Art
There is an ultrasonic flowmeter that measures a flow rate of a fluid flow in pipe through the use of an ultrasonic wave. An ultrasonic flowmeter described in JP 2001-356032 A has a sensor part. The sensor part is attached to an outer surface of the pipe to transmit the ultrasonic wave to the fluid in the pipe from the sensor part. The ultrasonic wave propagated in the fluid is received by the sensor part. The flow rate of the fluid flow in the pipe is calculated, based on a time when the ultrasonic wave is propagated in the fluid.
In the above-described ultrasonic flowmeter, the time required from the transmission to the reception of the ultrasonic wave differs, depending on a dimension and a material of the pipe, a sonic speed in the fluid, a temperature, a density, and a kinetic viscosity of the fluid, and the like. Thus, for accurately calculating the flow rate of the fluid, various parameters regarding characteristics of the pipe and the fluid are required.
Accordingly, a user needs to perform complicated operation to set the various parameters, which imposes a large burden on the user. Moreover, it is difficult for a user having poor knowledge regarding such setting to properly make various settings.
On the other hand, as in a case where an operational state of a facility in a factory is managed, there is a case where an exact value of the flow rate of the fluid flow in the pipe is not required, but whether or not the fluid is flowing in the pipe at a flow rate equal to or larger than a predetermined value only needs to be detected. In such a case, in place of a flowmeter, a flow switch that outputs an on/off signal can be used. The flow switch is required to be usable by simple setting operation without requiring expert knowledge and complicated operation.